1. Field of the Invention
The present invention relates to organopolysiloxanes comprising polyhydroxyorganyl radicals, especially sugar radicals or sugar-derivative radicals, and polyoxyalkylene radicals, to processes for their preparation and to their use.
2. Description of the Related Art
Reaction products of siloxanes and sugars and/or sugar derivatives, and processes for their preparation, as well as their use in surfactant applications in the production of glass fibers, or for modifying contact lenses, are known. Various synthesis paths for the linking (hydrophilic) sugar radicals to appropriate functional siloxanes by way of hydrolysis-stable Si--C bonds are described in the technical and patent literature.
AT-A-393 509, for example, describes the synthesis of saccharide-modified siloxane compounds by hydrosilylating organohydridosiloxanes with saccharides that contain C--C multiple bonds. This method, however, has the disadvantage that the reaction proceeds selectively only in the presence of protective groups.
A reaction of amino-functional polysiloxanes with sugar lactones is the subject of DE-A-43 18 539. The resulting linkage via an amide bond, however, is of only limited stability to hydrolysis when these materials are used in aqueous media.
FR-A-2 646 672 describes the reaction of epoxy-functional polysiloxanes with sugar derivatives, such as gluconic acid. Here again, the use of these materials in aqueous media is limited by the sensitivity of the ester bond to hydrolysis.
A further option starts from hydroxyalkylsiloxanes, which are reacted with saccharides in an acid-catalyzed glycosidation reaction as described, for example, in DE-A-43 06 041. In this described mode of reaction, however, it is necessary to operate with an excess of hydroxyalkylsiloxane in order to obtain the defined products with low degrees of glycosidation. The excess hydroxyalkylsiloxane cannot be separated off and remains in the product, where under certain circumstances it may adversely affect the desired properties of the sugar siloxane. In addition, the use of the acidic catalyst induces degradation reactions on the siloxane chain.
DE-A-43 18 537 claims various routes for preparing siloxanyl-modified polyhydroxylated hydrocarbons, such as the hydrosilylation of propynyl glucoside with SiH-sil(ox)anes or the reaction of epoxy-functional di- and trisiloxanes with sugar amines, such as glucamine. The synthesis routes indicated here again have the problem that it is necessary first of all to overcome the pronounced difference in polarity between the (hydrophilic) sugar radical and the (hydrophobic) siloxane radical. For this purpose a description is given of multistage synthesis paths, having recourse, inter alia, to known protective-group chemistry. The reaction times required to modify even siloxane compounds of low functionality and low molecular mass are already long, even if high temperatures, autoclave pressures and considerable amounts of solvent are used. As the molecular weight of the siloxanes increases, the problems in compatibility mount up in such a way that the reaction rates that can be achieved become negligibly small. Consequently, although the methods described might possess some preparative significance, their conversion to the industrial production scale appears impracticable for the reasons set out above.
The principle known from DE-A-43 06 041 is utilized by U.S. Pat. No. 5,428,142 to prepare silicone-based glycosides by reacting polyethersiloxanes in this case, as starting materials, with saccharides or saccharide derivatives in the presence of an acidic catalyst. Here, the reaction of the OH group of the polyether with the saccharide results in linkage via an acetal group, but with the polyether radical functioning only as a spacer between the siloxane skeleton and the sugar. This modification gives materials which possess good emollient properties, are substantive with respect to the hair and skin, and have inverse cloud points.
The methods of DE-A-43 06 041 have additional disadvantages. For instance, the methods described in this patent for preparing siloxane glycosides are characterized by low rates of reaction, as are commonly observed in the case of polyethersiloxanes containing long-chain and/or terminally secondary OH-functional polyether radicals. This leads to uneconomical long reaction times or to high temperature stresses, both of which impair the color and properties of the resulting products. Here again, the use of the acidic catalyst may induce degradation reactions on the siloxane chain. In addition, the method indicated is restricted to only OH-functional silicone polyethers as starting materials. Reactions with terminally capped silicone polyethers, which are modified at the ends and carry, for example, a polar ester or ether group, are in principle not possible.
The task was to overcome the disadvantages described above, and the various further disadvantages known from the prior art, in relation to the synthesis of siloxane-sugar derivatives.